/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型vector
     */
    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> ans;
        dfs(root, &ans);
        return ans;
    }

    void dfs(TreeNode* node, vector<int>* array) {
        if (node) {
            dfs(node->left, array);
            dfs(node->right, array);
            array->push_back(node->val);
        }
    }
};